1. Field of the Invention
This invention relates to rotary grinding and shredding apparatus particularly of the large types which are employed for grinding up and shredding heterogenous refuse, such as municipal waste, into an almost pulverized constituency.
2. Description of the Prior Art
Rotary crushers and grinders have been in use for many decades. Originally such apparatus was developed and utilized in ore crushing operations to enable mining operators and ore processors more easily to extract metals from ore brought out of the earth. Such crushers and grinders would employ some type of heavy cylinder from the surface of which would project a plurality of blunt heads or feet. The ore would be passed between such a cylinder and an adjacent steel wall so that the ore lumps would effectively be hammered against such wall into small enough pieces to pass between the hammers and the wall and on to further processing.
In more recent decades variations of such apparatus have been devised and utilized for the purpose of shredding waste paper and also for breaking up into small components municipal or other waste materials. Municipal waste may consist of a wide variety of discarded items such, for example, as newspapers, cans, boards, wooden and cardboard boxes, broken metal garden furniture, concrete lumps, flower pots, brush, bottles, etc. Apparatus of this type are sometimes called "grinders", "shredders" or "hoggers". A number of models of one such apparatus have been made and sold for a number of years by Enterprise Company of Santa Ana, Calif. and have included as their single horizontal rotating element an axle or shaft upon which are mounted fixedly at varying angles about the shaft axis a series of heavy thick cross-shaped plates spaced from each other. Between each pair of such plates are rotatably mounted a plurality of hammer members with their axes of rotation disposed near the outer extremities of the plates and at points distributed about the shaft axis in such a manner that the axes of rotation of the hammers do not lie in rows, but are spiraled in their disposition about the surface of a projected cylinder coaxial with the shaft. As each part of this element rotates downwardly, its hammers pass downwardly close to a parallelly disposed grating below the element. When refuse is dropped onto the rotating element, it is carried by the latter into a small space separating the element's swinging hammers from the grating where the refuse is then pounded and crushed into small enough particles to pass out through such space to a discharge area.
While such grinders, shredders or hoggers have been very effective in reducing large grindable materials and refuse to relatively small components, several problems have arisen in connection with the operation of such apparatus, namely:
a. Care must be taken to prevent such feeding surges of materials or refuse into the space between the rotating element and the grating as may cause the motor driving the element in rotation to stall. When this occurs, the motor must be turned off and the operator of the apparatus must climb or reach in and throw out by hand a good part of the accumulated refuse which has thus caused the motor to stall.
b. Often refuse components are found to have slipped through between the hammers and grating in sizes which are considered still too large. To remedy this, the oversize items must be picked out of the discharge area and re-run through the apparatus.
c. In order to avoid surges which would stall the apparatus, it has been found desirable to curtail the tonnage of refuse which is dumped into the apparatus' hopper during a given period of time. Such curtailment could require the installation of a second machine in order to enable a plant or facility to process all of the tonnage required to be processed.
d. Occasionally uncrushable objects, such as a cast iron engine block, might be included among refuse being ground. This might not only cause the motor to stall when the item becomes wedged in between the hammer and the surrounding grating, but it might also damage the grating, the hammers or other parts of the apparatus.
e. The cross-shaped plates have been heavy and, as such, have been expensive and difficult to install.
f. Heretofore, the cross-shaping has been felt necessary in order to permit access to pins holding the hammers for their installation and replacement. However, such cross-shaping has tended to prevent the development of smooth inertial force in the rotating element, which force is important in overcoming refuse surges. Instead, there is more of a tendency towards a flywheel effect.
Other manufacturers of this type of equipment have adopted different designs for their rotating elements, such manufacturers being Allis-Chalmers, Inc. of Milwaukee, Wis.; Grundler Company, St. Louis, Mo.; American Pulverizer Co. of St. Louis, Mo.; Williams Patent Crusher Co., of St. Louis, Mo.; and Jacksonville Blowhog, Inc., of Jacksonville, Fla. None of the equipment of such other manufacturers, however, overcomes all of the problems described above. Thus, each of these differently designed shredders, grinders, crushers or hoggers, presents one or more of the problems itemized above, and usually others, depending upon the particular design involved.